LOS ANGELES (AP) — A California congresswoman has asked for a moratorium on offshore fracking after reports that the controversial oil and gas extraction process has been used in coastal waters for decades.

Fracking, or hydraulic fracturing, in federal waters off the coast should be halted until there's a study to determine its impact on the environment and public health, Rep. Lois Capps said in a letter sent Tuesday to U.S. Interior Secretary Sally Jewell and Environmental Protection Agency Administrator Gina McCarthy.

There has been "inadequate oversight" of offshore fracking, and all current and proposed fracking projects should be halted pending a comprehensive review, Capps said in the letter.

Fracking involves pumping huge amounts of water, sand and chemicals into deep rock formations or old wells to release oil or natural gas. While the state oversees oil wells, there have not been specific rules for fracking.

Little is known about the effects on the marine environment of fracking, and neither state nor federal environmental regulators have had any role in overseeing the practice as it has increased to revitalize old wells.

The call for a moratorium is unsurprising but unnecessary, said Tupper Hull, spokesman for the Western States Petroleum Association, whose members produce 80 percent of California's oil.

"Hydraulic fracturing as used in California is a well-understood technology. It is proved to be safe. It has never been associated with any environmental harm of any kind," he said Thursday.

Oil companies have used fracking at least 203 times at six California sites in the past two decades, including waters off some of the region's most popular surfing strands and tourist attractions, according to interviews and drilling records obtained by The Associated Press.

Those figures include fracks this year on man-made drilling platforms inside Long Beach Harbor rather than in waters farther out to sea. However, other companies fracked more than a dozen times from old oil platforms off Huntington Beach and Seal Beach over the past five years.

Though there is no evidence offshore hydraulic fracturing has led to any spills or chemical leaks, the practice occurs with little state or federal oversight.

However, the handling of water "of any kind" requires federal pollution-control permits, and the process is so strict that even rainwater falling on California offshore oil platforms is captured and treated onshore, said Hull, the petroleum association spokesman.

But Capps said she is bothered by the unknowns.

"We know virtually nothing about the size of these fracks, the chemicals being used, or the impacts on the marine environment. They have been approved with categorical exemptions and decades-old permits that are woefully inadequate," the Democrat said in a speech on the House floor Tuesday.

Capps was speaking out against two proposed House bills on fracking — H.R. 2728 and H.R. 1965 — that she contends would weaken environmental protections.

The bills are "reckless giveaways to big oil and gas companies that put American families and the environment at risk," Capps argued.